There are many common causes of knee pain – you will need to get checked up and examined by a doctor.
Some pertinent questions in your situation – any other joints affected, how long you’ve had the pain for, any prior trauma or injury, whether you have a background as a frequent runner etc, can all sway the according possible diagnoses your doctor will have. He will know which questions to ask you to tease this information out.
The fact that you are female and in your 30s would also make me more inclined to rule out some types of auto immune conditions which affect the joints, such as rheumatoid arthritis/SLE etc; especially if you have more than one joint that’s affected, or a family history of autoimmune medical conditions.
Any of the other structures around your knee can also contribute to the pain – this includes the bone, ligaments, and muscle. Examples of common conditions among people with knee cap area pain include Patellofemoral pain syndrome (I suspect this from your story), Patellar tendinitis, Bursitis, or a sprained ligament. Osteoarthritis is also another common cause of resting knee pain (as you’ve described), but it’s more common after the age of 50s, unless you had an injury to the knee before.
When you see your doctor, he will be able to better advise you on what condition you may have, and perform the correct examinations. If necessary, he may also request for an X-ray or an MRI for your knee.
In the interim, you should rest your knee and ice it where possible. Sparing use of oral anti-inflammatories, such as Ibuprofen, will also help with your knee pain. You could also try applying a topical NSAID (Fastum gel) to your knee for pain relief.
Cheers
